Additive manufacturing device and method

ABSTRACT

Disclosed is an additive manufacturing device, comprising: a vessel for containing a material which is polymerisable on exposure to radiation; a build platform having a build surface, the build platform being mounted or mountable for movement relative to the vessel; and a programmable radiation module comprising an array of individually addressable radiation emitting or transmitting elements, the array being configurable to produce radiation having a predetermined pattern by selective activation of elements of the array; wherein the programmable radiation module is positioned or positionable to irradiate uncured material adjacent the build surface, or adjacent a previously cured structure on the build surface, with the predetermined pattern without magnification. Also disclosed is an additive manufacturing method which employs the additive manufacturing device.

TECHNICAL FIELD

This invention relates to a stereolithographic method of additivemanufacturing that allows for high speed printing of large objects, atfine resolution, and to a device for carrying out the method.

BACKGROUND

A typical stereolithographic additive manufacturing device involves asource of radiation and a means of directing that radiation inaccordance with specific patterns onto a layer of polymerizablematerial. The radiation causes this material to polymerize, i.e., to atleast partially solidify. A common type of stereolithographic additivemanufacturing machine utilizes a laser which emits a collimated beam ofradiation in the ultraviolet or near-ultraviolet range of theelectromagnetic spectrum. The process of manufacturing athree-dimensional part with such an additive manufacturing apparatus maycomprise the following steps:

1. A mirror, lens or assembly of optical components is used to directthe laser beam in accordance with pre-determined patterns. In this typeof machine, there is at least one mirror or lens which may beelectronically actuated to move in order for the optical assembly to becapable of altering the direction of the laser beam.2. The point where the laser beam strikes the layer of polymerizablematerial travels along a scan path such that all regions wherepolymerization is desired will be illuminated by the laser beam for asufficiently long amount of time to cause the polymerization.3. When each of the desired regions in a given layer of material havebeen polymerized, an assembly of mechanical and/or electrical componentsis capable of depositing a new layer of such polymerizable material ontop the last polymerized layer, and the cycle repeats.

Each layer may have a different pre-determined pattern and the laserbeam is capable of travelling along the path required to polymerize eachof the regions in such a pattern, so that three-dimensional objects ofvarying cross-sections may be produced using the additive manufacturingdevice.

A major disadvantage of the prior art stereolithographic method ofadditive manufacturing is that it is slow. The laser beam must travelalong a path so as to illuminate all regions of the layer of materialwhere polymerization is desired. For a laser beam having a fixed widthand a constant speed of travel, the time required to print an objectincreases linearly with the dimensions of said object and the density ornumber of features in a given layer. A scanning laser stereolithographicprinting device can achieve a certain maximum scanning speed, i.e., ifthe printable area is doubled, the scanning laser would take twice aslong to cure one layer of that area.

An evolution of the stereolithographic process described above is one inwhich the laser beam and optical assembly are replaced by a DigitalMicromirror Device (DMD) projection device, capable of renderingmonochromatic images using electronically addressable reflectors. Suchadditive manufacturing devices offer the possibility of “layer-by-layer”as opposed to “dot-by-dot” printing, i.e. high speed printing. Thetypical system comprises what is essentially an overhead projectorhaving a digital micromirror device (DMD) and a light source which emitsat least some ultraviolet light. The projector projects an image (e.g.white on black background, where white regions are illuminated by lightwhich is at least partially ultraviolet) onto a layer of photoactiveresin, such that the white areas of the image will cure as a result ofthe incident UV light. Currently, DMD chips having resolutions of up to1920×1080 pixels can be manufactured, thus allowing for very rapidlayer-by-layer printing: a single exposure of a pattern image from aDMD-based projection system can cause polymerization in 1920×1080 (over2 million) small regions of polymerizable material, whereas alaser-based system would require the single dot at the end of its laserbeam to travel along a path illuminating each of the 2 million dotsindividually.

The main disadvantage of a DMD-chip based printing method is that thedimensions of the largest object that may be printed with such anapparatus is limited: If the projected area is enlarged (scaled), therewill be two disadvantages:

1. As the number of addressable pixels is fixed at a maximum of 2million, the projected image is stretched if a large object is to beprinted. To scale the image for a build size of 1 meter by 2 meters,each pixel would be stretched to occupy approximately 1 mm×1 mm, whichis far coarser than is acceptable for 3D printed object resolution.2. The curing time (exposure time required for polymerization to occur)increases significantly when the projected image is scaled for largebuild sizes. The light emitted from the same source (e.g. single bulb)must be distributed over a larger surface area, i.e. the total number ofphotons incident on a given amount of photoactive resin per unit time isreduced whenever the build size is scaled up.

The present invention seeks to overcome one or more of the abovedisadvantages, or at least to provide a useful alternative.

SUMMARY

Some embodiments relate to an additive manufacturing device, comprising:

-   -   a vessel for containing a material which is polymerisable on        exposure to radiation;    -   a build platform having a build surface, the build platform        being mounted or mountable for movement relative to the vessel;        and    -   a programmable radiation module comprising an array of        individually addressable radiation emitting or transmitting        elements, the array being configurable to produce radiation        having a predetermined pattern by selective activation of        elements of the array;    -   wherein the programmable radiation module is positioned or        positionable to irradiate uncured material adjacent the build        surface, or adjacent a previously cured structure on the build        surface, with the predetermined pattern without magnification.

Other embodiments relate to an additive manufacturing method,comprising:

-   -   at least partially filling a vessel with a material which is        polymerisable on exposure to radiation;    -   providing a programmable radiation module comprising an array of        individually addressable radiation emitting or transmitting        elements;    -   providing a build platform having a build surface;    -   positioning the build platform relative to the vessel such that        an uncured layer of polymerisable material is defined between        the build surface and the programmable radiation module; and    -   irradiating the uncured layer of polymerisable material with        radiation having a predetermined pattern, without magnification,        by selectively activating elements of the array of the        programmable radiation module in order to polymerise the uncured        layer with the predetermined pattern.

The patterned radiation produced by the programmable radiation moduleallows layer-by-layer curing of the polymerisable material in thevessel, thus providing faster and more scalable production ofthree-dimensional structures than prior art arrangements which usescanning lasers. In particular, the achievable printing speed isindependent of the layer thickness and resolution. An inherent problemin many other 3D printing technologies is the need to strike a balancebetween desired resolution and desired printing speed: if a userrequires a finer vertical resolution, e.g. twice as thin layers, theprint job will take twice as much time, as the printing speed is limitedby the speed at which the scanning laser can move. In embodiments of thepresent invention, making the layers twice as thin means that each layercan be cured with a pulse of light that is less than half as long (asthere is half as much polymerizable material by volume present to becured). The overall print job duration for the object is thereforeindependent of layer thickness. The same principle applies to X-Yresolution, which is only controlled by the resolution (as measured indots per inch, for example) of the addressable array of the radiationmodule.

An additional advantage with respect to scanning laser systems is thereduction in moving parts. As there is no scanning laser, the buildtable is the only component that is mechanically actuated, resulting inlower costs and greater durability.

Further, by irradiating the uncured fluid without magnification (i.e.,with a substantially 1:1 magnification ratio), it is possible to avoidcertain disadvantages of DLP projection based systems. In particular, inorder to scale up to larger print sizes, a DLP projector needs toincrease the projected area, thereby lowering the intensity ofillumination per unit surface area and thus increasing the cure time.

In some embodiments, the programmable radiation module comprises aliquid crystal display (LCD) containing the array of individuallyaddressable radiation transmitting elements, the radiation transmittingelements in this case being the pixels of the LCD. The use of an LCD isparticularly advantageous since LCD units are orders of magnitude lessexpensive than DLP projectors.

Preferably, the LCD is a monochrome LCD. For printing applications,light in the ultraviolet (UV) or true violet (TV) range is mosteffective, as each photon carries a relatively large amount of energy.The wavelength for these photons ranges from approx 300-450 nm. All ofthe sub-pixel colour filters (R, G, and B) in a colour LCD prevent mostof the light of such wavelengths from passing through them, i.e. theintensity of effective photons transmitted through a normal LCD isminimal. For this reason, the use of a monochrome LCD, which does nothave any colour filters, has been found to give much shorter curing time(more photons of suitable wavelength are transmitted).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way ofnon-limiting example only, with reference to the accompanying drawingsin which:

FIG. 1 shows an exploded cross-sectional view of an additivemanufacturing device according to some embodiments of the invention;

FIG. 2 shows a cross-sectional view of the device of FIG. 1, and furthershowing a build platform of the device;

FIG. 3 shows the device of FIG. 1 and FIG. 2 during use, with a firstlayer of a three-dimensional object being polymerized;

FIG. 4 shows the device of FIG. 1 and FIG. 2 during use, with asubsequent layer of the object being polymerized;

FIGS. 5A, 5B and 5C illustrate an additive manufacturing deviceaccording to some embodiments, in which a completed model is separatedfrom a build platform by peeling;

FIGS. 5D and 5E illustrate an additive manufacturing device according toother embodiments, in which a completed model is separated from a buildplatform by peeling;

FIGS. 6A and 6B illustrate an additive manufacturing device according tofurther embodiments, in which a completed model is separated from abuild platform by shearing;

FIGS. 6C and 6D illustrate an additive manufacturing device according toyet further embodiments, in which a completed model is separated from abuild platform by shearing;

FIG. 6E illustrates an additive manufacturing device according to yetfurther embodiments, in which a completed model is separate from a buildplatform by shearing;

FIG. 7 is a block diagram of an exemplary control system for an additivemanufacturing device according to embodiments;

FIG. 8 is a block diagram of software components of the control systemof FIG. 7;

FIG. 9 is a flow diagram of an additive manufacturing process accordingto some embodiments; and

FIG. 10 is a flow diagram of an additive manufacturing process accordingto other embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

In certain embodiments, an additive manufacturing device comprises aradiation source (such as a stroboscopic light source emitting visiblelight having a wavelength of 400-700 nm) on top of which is mounted aliquid crystal display, e.g. a diffuser assembly comprising one or moresheets with diffusive properties, followed by two polarizing panels atright angles to each other, the polarizing panels sandwiching a layer ofliquid crystals. The liquid crystal display (LCD) assembly may becovered with a glass or transparent plastic panel and a layer oftransparent silicone or other cure-inhibiting or low friction material.

The above arrangement can achieve printing speeds in excess of scanninglaser systems, since an entire layer is exposed in a single pulse ofstroboscopic light, whereas a scanning laser must scan the entire paththat is to be cured. In the presently described embodiments, theprinting speed per layer is independent of the number of features (orsurface area) to be cured in each layer. Unlike with scanning lasers, inthe presently described embodiments it takes an equally long pulse oflight to cure the entire full solid layer as it does to cure a smallshape within that area. LCD panels can presently be manufactured to verylarge sizes (to the order of meters in length and width dimensions) andincreasingly high resolutions (in excess of 16 million pixels), thus thelayer-by-layer printing technology of at least some embodiments isbetter scalable and capable of printing larger objects at finerresolution than DMD-based systems.

Referring now to FIG. 1, there is shown a schematic exploded view of anadditive manufacturing device 100 according to some embodiments of theinvention. The additive manufacturing device 100 comprises a vessel 1for containing a polymerizable material 40. The vessel 1 has atransparent lower wall 11, sidewalls 102 and a seal 2 between thetransparent lower wall 11 and the sidewalls 102 of vessel 1. The sealmay be formed from a material such as epoxy which is cured in situ toseal the vessel, but it could also be a solid seal such as a rubber(nitrile or viton, for example) O-ring or gasket. Preferably, the vessel1 has four sidewalls defining a rectangular or square internal region,but it may of course have a single cylindrical sidewall or otherconfiguration.

The device 100 may further comprise a rigid transparent member 3 whichprovides structural strength to vessel 1, though this may be omitted iflower wall 11 is sufficiently sturdy. Underneath rigid transparentmember 3, a liquid crystal display (LCD) 5 is sandwiched between a firstpolarizer panel 4 and a second polarizer panel 6. The direction ofpolarization of the first polarizer panel 4 is perpendicular to that ofthe second polarizer panel 6. Below the second polarizer panel 6 theremay be provided an optical assembly 7 which may comprise various opticalcomponents capable of diffusing, collimating, reflecting or refractinglight from a light source 8. Typically the optically assembly 7 includesdiffusing and collimating elements.

The LCD 5, polarisers 4 and 6, and light source 8, and optical assembly7 form part of a programmable radiation module 10 (FIG. 2) which isattached to the transparent lower wall 11 of the vessel 1 and which canbe configured to produce a patterned beam of radiation to cure a layerof resin in the vessel 1 with a desired pattern. The pixels of LCD 5constitute individually addressable elements which may be switched on oroff by a control system of the device 100, which is coupled to the LCD 5(as shown in FIG. 7). When a pixel is activated (switched on), it allowslight to be transmitted through it, whereas when it is inactive(switched off), it blocks light. Accordingly, the pixels of LCD 5 areindividually addressable light transmitters which can be programmed bythe control system to produce the desired pattern of radiation, with theinactive pixels acting as masking elements.

The LCD 5 is preferably a monochrome LCD. In a colour LCD, each pixel ismade up of three or four individually addressable sub-pixels, eachhaving a colour filter that allows light in a narrow wavelength band topass through it. The panchromatic white backlight in a colour LCD emitsall wavelengths between 400-700 nm, and colour is created by selectivelyallowing this white light to pass through the red, green and blue(R,G,B) filtered sub-pixels. For printing applications, light in theultraviolet (UV) or true violet (TV) range is most effective, as eachphoton carries a relatively large amount of energy. The wavelength forthese photons ranges from approx 300-450 nm. All of the sub-pixelfilters (R, G, and B) in a colour LCD prevent light of such wavelengthsfrom passing through it, i.e. the intensity of effective photonstransmitted through a normal LCD is minimal. For this reason, the use ofa monochrome LCD, which does not have any colour filters, has been foundto give much shorter curing time (more photons transmitted).

In some embodiments, the radiation module may comprise a panel ofindividually addressable light emitters in an array, such as an LED orOLED display. In similar fashion to the LCD 5, the panel can beprogrammed by the controller such that selected light emitters areactive at any given time, in order to produce the desired pattern ofradiation. In these embodiments, the individually addressable elementsof the radiation module themselves emit the radiation in the desiredcuring pattern, rather than acting as a mask for a separate radiationsource. LEDs and Organic LEDs can in principle be designed to emit anyparticular wavelength of light (visible, UV, IR) to match the specificcuring requirement of the polymerisable fluid. In these embodiments, theadditive manufacturing device could be made more compact as no“backlight” as such is required when the display panel itself is thelight source, and the need for an optical assembly between the separatelight source and LCD is also eliminated.

In the configuration shown in FIG. 1, the radiation module 10 isattached to the lower wall 11 and sidewalls 102 of the vessel 1.However, in alternative embodiments, the radiation module 10 may belocated within or be integral to the vessel 1. For example, thesidewalls 102 and lower wall 11 may be aluminium plates which are weldedtogether to form the vessel 1 (with the lower wall 11 in this caseobviously not being transparent), and the radiation module 10 may thenbe placed inside the vessel 1. A transparent sealing layer may be placedover the top of the radiation module 10 to prevent leakage ofpolymerizable material into the radiation module 10, for example.

The array of pixels of LCD 5 may be sized to cover substantially theentire surface area of the transparent lower wall 11, such thatsubstantially the entire volume above the transparent lower wall 11 is aprintable volume. In alternative embodiments, the pixel array may covera surface area which is smaller than the surface area of transparentlower wall 11. For example, the pixel array may have a surface areaequal to or slightly larger than that of the build surface 92 of thebuild platform 9, such that the perimeter of the build surface 92 fitsinside the perimeter of the pixel array.

Referring now to FIG. 2, the mechanical assembly which renders theadditive manufacturing device 100 capable of producing multi-layeredobjects is shown in more detail. As shown in FIG. 2, the device 100comprises a build platform 9 having a build surface 92. The buildsurface 92 faces towards the lower wall 11 of vessel 1. The buildplatform 9 is suspended inside the vessel 1 above the lower wall 11 andthe radiation module 10.

Build platform 9 is capable of moving or being made to move verticallyupward and downward relative to vessel 1 above the lower wall 11, bymeans of a mechanical assembly 20 which may comprise ball screws, leadscrews, belt drive mechanisms, a chain and sprocket mechanism, or acombination thereof, and a precision stepper motor 21. In a preferredembodiment, the movement mechanism comprises threaded rods and steppermotor 21, which is driven by a microcontroller 270 of a control system200 of the device 100 (FIG. 7) and which can provide 5 μm precision inthe vertical position of the build platform 9. The combined mechanicalassembly 20 and stepper motor 21 are fixed upon or connected to a frame22 which is supported on sidewalls 102. The frame 22 provides rigidsupport and a reference point for the vertical position of the buildplatform 9. Greater precision (up to about 1 μm) may also be achievedthrough a suitable choice of lead screw or belt pitch and the resolution(steps per full revolution) of the stepper motor.

FIG. 3 and FIG. 4 illustrate an exemplary build process for athree-dimensional object 42. In FIG. 3, the vessel 1 is partially filledwith a polymerizable material 40, such as a polymerizable resin. Next,the build platform is moved upwardly within the vessel 1 using thestepper motor 21 to actuate mechanical assembly 20, to define a thinlayer 30 of the polymerizable material between the lower surface 92 ofthe build platform and the transparent lower wall 11 of the vessel 1.The layer 30 has a thickness chosen according to the desired resolutionalong the z-axis. Once the layer of uncured material 30 has beendefined, radiation module 10 irradiates the layer 30 through thetransparent lower wall 11 of vessel 1 with a predetermined pattern (asdescribed above) so as to selectively polymerize desired areas of thethin layer of polymerizable material 30 with the predetermined pattern.

The transparent lower wall 11 may have a cure-inhibiting or non-stickcoating so that the polymerized material does not adhere to it. Inparticular, the coating can be chosen so that the friction and/oradhesion between the transparent lower wall 11 and the polymerizedmaterial is less than the friction and/or adhesion between the buildsurface 92 and the polymerized material. Accordingly, when the steppermotor 21 actuates the assembly 20 to move the build platform 9 upwardsfor curing of the next layer of object 42, the polymerized material willtend to move with the build platform 9 instead of being pulled free dueto adhesion to lower wall 11.

In some embodiments, a silicone sheet may be provided on the transparentlower wall 11. The cured portions of the printed object 42 will tend toadhere to the build platform (as the build platform is preferablyfabricated of aluminium, acrylic, polycarbonate or other plastic towhich the cured material adheres well) while the material does notadhere to the silicone sheet. A silicone sheet is preferred, as it istransparent and non-consumable. The non-stick coating is preferably madeas thin as possible, since a thinner layer between the LCD (mask) andthe material to be cured (resin/polymer/adhesive) means that there isless divergence of the light transmitted from the LCD before it reachesthe resin/polymer/adhesive, thus resulting in a physical printingresolution closer to the LCD (mask) resolution.

In other embodiments, liquid coatings including mould release agentssuch as CHEMLEASE (registered trade mark) of Chem-Trend LP of Michigan,or solid sheets or coatings such as polyurethane,polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) orlatex can be used, so long as the material is transparent to thewavelength of light being used as a curing initiator and can be madesufficiently thin so as to prevent substantial resolution loss betweenthe liquid crystal display resolution and the physical printingresolution. FEP is particularly preferred as it tends to be moretransparent than PTFE at most curing wavelengths.

If a coating is used, it should be chosen to minimize divergence of thebeam produced by a pixel of the radiation module 10 as the beamundergoes refraction through the coating. In particular, at the pointwhere it reaches the layer of polymerizable material which is to becured, the beam should cover an area which is less than four times thepixel surface area (e.g., for an LCD with pixels measuring 50×50microns, the light passing through that pixel should not be larger than100×100 microns when it reaches the layer). If it is any larger, it willoverlap the beams produced by its neighbouring pixels by more than 25microns, i.e. more than halfway into the neighbouring pixels, such thatthe neighbouring pixels are no longer resolvable. Preferably, thecoating(s) result in pixel beams at the curing layer which have asurface area which is no more than 1.2× the LCD pixel surface area. Thiscan be achieved by making the coatings very thin, and collimating thelight prior to it passing through the LCD, so that the beam travellingthrough the LCD pixel is less divergent. For example, if a PTFE or FEPsheet is used as the coating, it may be have a thickness ofapproximately 70 μm. A thickness of under 50 μm may also be used.Typically, a coating thickness which is less than or equal to thepixel-to-pixel distance (resolution of the LCD) is desirable.

After polymerization of a layer is completed as discussed above inrelation to FIG. 3, the mechanical assembly 20 is actuated by precisionstepper motor 21 so that build platform 9 is raised upward by a smallamount (equal to the desired layer thickness) relative to a referencepoint on frame 22 such that a void is created between the lastpolymerized layer and the top surface of the transparent lower wall 11of the vessel. This void is rapidly filled by surrounding polymerizablematerial, which flows into the void under gravity, so that a new thinlayer of such material exists between the bottom surface of the lastpolymerized layer and the top surface of the transparent lower wall 11of vessel 1. This new layer of polymerizable material is irradiated frombelow by radiation module 10 so as to selectively polymerize a desiredarea using a pattern of radiation defined by active area 32 of the LCD 5(i.e., an area which is unmasked due to pixels in that area beingactive), as shown in FIG. 4. As resin 40 is consumed, fresh resin may beadded to replenish the vessel 1. Repeating this process for eachsubsequent layer and allowing desired area 32 to have any shape ornumber of shapes allows this additive manufacturing apparatus to producea three-dimensional object having any shape, dimension or complexitywithin the boundaries of vessel 1 and the range of motion of buildplatform 9 as permitted by mechanical assembly 20.

In some embodiments, the device 100 may be configured such that thebuild surface is on the upper surface, rather than the lower surface, ofthe build platform 9. In these embodiments, the programmable radiationmodule 10 is positioned at the top of the vessel 1. During a buildprocess, the build platform 9 starts with the build surface at the topof the fluid level in the vessel 1, and descends within the vessel 1 todefine a thin layer of uncured material which is then cured by radiationmodule 10 in a desired pattern as previously described. The buildplatform 9 progressively descends within the vessel 1 in steps of thedesired layer thickness, with each layer being cured with the respectivedesired layer pattern. The device of these alternative embodiments isvery similar in construction to the device 100 shown in FIG. 1 to FIG.4, except that in use, the vessel 1 needs to be filled withpolymerizable material up to at least the height of the final object 42.Since the build surface in these arrangements may be spaced from the topsurface of the vessel 1 and the radiation module 10, a non-stick coatingmay not be required on the top surface.

In the device 100 of FIGS. 1-4, as described above, the transparentlower wall 11 may have a cure-inhibiting or non-stick coating so thatwhen a layer is cured, the build platform 9 can simply be moved up inorder to separate the cured layer from the transparent lower wall 11 toenable curing of the next layer. If a non-stick layer is not provided,alternative mechanisms for separating the most recently cured layer fromthe vessel or the radiation module may be employed, as illustrated inFIG. 5A to FIG. 5E and FIG. 6A to FIG. 6E.

In FIG. 5A, an additive manufacturing device 500 comprises a vessel inthe form of a basin 50 which contains a polymerizable fluid 51. A buildplatform 70 having a lower build surface 71 is submerged inside thebasin 50. The build platform 70 is vertically movable relative to thebasin 50 by a mechanism similar to that described above, except that themechanical assembly 20 and stepper motor 21 may be mounted to a supportframe which is separate from the basin 50. A thin layer of polymerizablefluid 51 is defined between build surface 71 and the contact surface ofa programmable radiation module 60, which is capable of emittingpatterned light of suitable wavelength to initiate the polymerization(curing) of fluid 51. The radiation module 60 may be substantially thesame as the radiation module 10 described above, for example.

The basin 50 is pivotable about point 53. After a layer of fluid 51 hasbeen cured to form part of a printed object 52, the basin 50 pivotsabout point 53, as shown in FIG. 5B, so as to “peel” the recently curedlayer off the face of the radiation module 60. If the radiation module60 is separate from the basin 50, with the basin 50 having a transparentlower wall (as described above), the pivoting movement of the basin 50acts to peel the recently cured layer from the transparent internalbottom face of the basin. In some embodiments, rather than the basin 50being pivotable, the build platform 70 may be pivotable about itssupport.

As shown in FIG. 5C, the amount of polymerizable fluid 51 required toprint a given object 52 using the device 500 is relatively small,because the curing process always takes place at the bottom of basin 50when the radiation module 60 is mounted below the basin, irradiatingupward. As polymerisable fluid 51 is consumed during a printingoperation, additional fluid may be added to vessel 50, for example bypumping it into the vessel 50. A level sensor (not shown) may be used toprovide a feedback signal to the control system 200 (FIG. 7) of thedevice 500 that additional fluid is required, and the control system200, via microcontroller 270, may then actuate a pump (not shown) topump a desired volume of fluid into vessel 50.

In the arrangement of FIG. 5D, an alternative additive manufacturingdevice comprises a basin 50 containing polymerizable fluid 51, a thinlayer of which is defined between the last polymerized layer and thecontact surface of radiation module 60, which is partially immersed inthe polymerizable fluid 51, and which irradiates the thin polymerizablefluid layer from above. After a given layer of fluid is polymerized, theradiation module 60 may pivot about point 54 so as to “peel” the lastpolymerized layer off the radiation module's contact surface. As for thearrangement of FIG. 5A-5C, rather than the basin 50 being pivotable, thebuild platform 70 may be pivotable about its support.

In the arrangement of FIG. 5D and FIG. 5E, the printed object ispositioned on top of build surface 71 of build platform 70, so that theweight of the printed object 52 assists (rather than counteracting) theseparation (peeling) of the last cured layer from the radiation module60 contact surface.

Turning now to FIG. 6A to FIG. 6C, there is shown a further example ofan additive manufacturing device 600, having a basin 50 of increasedwidth compared to the basin 50 of FIG. 5A to FIG. 5C. The basin 50 has afirst region 602 below which the radiation assembly 60 is positioned inorder to successively polymerize thin layers of fluid 51 in order tobuild up an object 52. The basin 50 also has a second region 602, havinggreater depth than the first region 602.

The device 600 comprises a build platform 70 which is capable of movingboth vertically and horizontally. After one layer of fluid 51 has beenpolymerized by irradiation from below in the first region 602, the buildplatform 70 moves laterally to the region 604 of basin 50 having greaterdepth than first region 602. Alternatively, the build platform 70 mayremain stationary while the basin 50 and radiation module 60 movelaterally (for example, on a translation stage to which the basin 50 andradiation module are coupled) until the region 604 is positioneddirectly underneath the build platform 70. This mechanism makes use ofthe fact that the adhesion forces between a recently polymerized layerand the contact surface of radiation module 60 are predominantlyvertical forces, i.e. far less friction is encountered by laterallysliding the printed object 52 off the contact surface into the deeperregion 604 of basin 50.

Once the platform 70 and printed object 52 have arrived at the deeperend 604, the vertical adhesion forces are no longer present and buildplatform 70 is capable of moving upward by a desired distance. Afterthis, the platform may move back (laterally) to the shallower region 602of the basin, again defining a thin layer of polymerizable fluid betweenthe last polymerized layer and the contact surface of the radiationmodule 60, so that this new layer may be polymerized.

As shown in FIG. 6C, the amount of polymerizable fluid 51 required toprint a given object 52 is relatively small, because the curing processalways takes place at the bottom of basin 50 when the radiation module60 is mounted below the basin, irradiating upward. Accordingly, objects52 of substantially greater height than that of the basin 50 may beprinted. Additional fluid 51 may be pumped into the vessel 50 by a pump,under feedback control using a level sensor of control system 200 ofdevice 600, as previously described.

Referring now to FIG. 6D and FIG. 6E, in a yet further embodiment of anadditive manufacturing device 650, a basin 50 containing polymerizablefluid 51 has a first region 652, and a second region 654 disposed nextto the first region 652, which is shallower than the first region 652.The device 650 comprises a build platform 70 which is capable ofvertical motion, and an radiation module 60 which is capable of lateral(sliding) motion. The radiation module 60 irradiates the polymerizablefluid 51 from above in first region 652 to create an object 52layer-by-layer on upper build surface 71 of build platform 70. A thinlayer of polymerizable fluid 51 is defined between the previouspolymerized layer and the contact surface of the radiation module 60.After this layer is cured by irradiating it from above, the radiationmodule 60 may move laterally to the shallower region 654 (FIG. 6E),after which build platform 70 may move downward into basin 50 by adesired distance corresponding to the desired layer thickness. Whenradiation module 60 slides back to its original position 652 a new layerof unpolymerized fluid is defined between its bottom contact surface andthe top of the last polymerized layer.

The radiation source of radiation module 10 or radiation module 60 maybe any radiation source suitable for curing the polymerizable material40 or 51, such as visible, UV or infrared light, or other actinicradiation, such as X-rays. The radiation source may be of any suitabledimension and have any number of optical components to collimate ordirect it at at least an area of the LCD panel 5, for example. Theradiation source may be movable or stationary.

In certain embodiments, the radiation source is a visible light (400-700nm) source. Some embodiments comprise a white LED stroboscopic lamp as aradiation source, as these lamps have peak intensities at 460 and 550nm. This is because white light as such cannot be created; instead theLED generates blue light (460 nm) and a phosphorus internal coatingabsorbs this partially and emits green (550 nm) such that the combinedemission appears to the human eye as white light. This light source issuited for visible-light polymerizable materials. In other embodiments,the radiation source may emit in the range 300-450 nm.

In some embodiments, UV light may be used as a radiation source.Advantageously, UV photons carry higher energy than visible lightphotons and many polymers are available that cure in UV light. If UVlight is used as the radiation source then it may be necessary to use adynamic mask generator other than an LCD since liquid crystals maydeteriorate when exposed to ultraviolet light. Alternative dynamic maskgenerators may comprise electrowetting displays, transmissiveelectrophoretic displays, and printers for continuously generatingphysical masks (e.g., continuous (ribbon) laser or inkjet printing oftransparencies).

An example of a control system 200 of the additive manufacturing devicesdescribed above is shown in FIG. 7. The control system 200 may include acomputer system 201 comprising standard computer components, includingnon-volatile storage (such as a hard disk or solid-state disk) 204,random access memory (RAM) 206, at least one processor 208, and externalinterfaces 210, 212, 214, 218, all interconnected by a bus 216. Theexternal interfaces include universal serial bus (USB) interfaces 210,and a network interface connector (NIC) 212 which connects the system201 to a communications network 220 such as the Internet, via which auser computer system 240 may communicate with the control system 200 toallow the user to interact with the device 100. The user computer system240 may be a standard desktop or laptop computer system, such as anIntel IA-32 based computer system, or a mobile computing device such asa smartphone or tablet computer. The control system 100 can receiveinput data via NIC 212 or from a storage device connected to one of theUSB interfaces 210, or to an alternative interface such as a securedigital (SD) interface (not shown).

In some embodiments, the user may interact directly with the computersystem 201, by means of a display, keyboard and mouse or otherinput/output devices connected via one of the interfaces 210, and anadditional display adapter (not shown). In alternative embodiments thecomputer system may comprise a touchscreen input/output device connectedto bus 216, for example by a display adapter (not shown). In theseembodiments, the user computer system 240 may be unnecessary. A 3D modelfile may be loaded onto the computer system 201 by the networkconnection 220 or SD card or USB storage connected via externalinterface(s) 210 and the user can then control the slicing processdirectly on the additive manufacturing device via e.g. the touch screeninterface of computer system 201.

The system 201 also includes a display adapter 214, which is used tocommunicate with the LCD 5. The display adapter 214 may be ahigh-definition multimedia interface (HDMI), video graphics array (VGA)or digital visual interface (DVI), for example.

The storage medium 204 may have stored thereon a number of standardsoftware modules, including an operating system 224 such as Linux orMicrosoft Windows, and one or more modules 202 comprising instructionsfor causing the at least one processor 208 to carry out variousoperations, including receiving input data relating to a 3D model(representing the object to be built) via USB interface(s) 210 and/ornetwork interface 212; processing the input data to generate a sequenceof layer patterns; and successively transmitting the layer patterns toLCD 5 (or alternatively, another type of dynamic mask generator or anLED or OLED display) via display adapter 214, and signaling amicrocontroller 270 to actuate mechanical, electrical and/or opticalcomponents of the additive manufacturing device. In some embodiments,the 3D model data may be provided in STL, STEP or another 3D vector fileformat, and stored on storage medium 204 for processing by module(s)202. In other embodiments the input 3D model data may be receivedlayer-by-layer from user computing system 240 or elsewhere viacommunications network 220 and stored either in RAM 206 or on storagemedium 204 for processing by module(s) 202.

Processes executed by the system 201 are implemented in the form ofprogramming instructions of one or more software modules or components202 stored on the storage medium 204 associated with the computer system201, as shown in FIG. 7. However, it will be apparent that the processescould alternatively be implemented, either in part or in their entirety,in the form of one or more dedicated hardware components, such asapplication-specific integrated circuits (ASICs), and/or in the form ofconfiguration data for configurable hardware components such as fieldprogrammable gate arrays (FPGAs), for example.

In one example, as shown in FIG. 8, the software components 202 comprisea master control component 280, which coordinates the overall flow of anadditive manufacturing process which is under the control of controlsystem 200. The master control component 280 is in communication with amechanical actuation component 286 which generates control signals todrive, via microcontroller 270, mechanical components of the additivemanufacturing device, such as pumps and motors. Master control component280 is also in communication with optical control component 288 whichgenerates control signals to (via microcontroller 270) turn theradiation source of radiation assembly 10 or 60 on or off, and tocontrol the duration and intensity of irradiation.

Master control component 280 may accept user input data, such as the 3Dmodel data, and build parameters such as the positioning and orientationof the object with respect to the build surface, arrangement of multipleobjects in the same batch print, and the desired print layer thickness(which determines how many slices need to be generated, etc.). The inputdata can then be passed to model processing component 282, which“slices” the 3D model data in accordance with the build parameters togenerate a sequence of two-dimensional image files, which can be storedon storage medium 204 for example. The model processing component maycomprise any known slicing software module, such as GnexLab,EnvisionLabs Creation Workshop, Slic3r or FreeSteel. Once the slicingoperation has been performed by model processing component 282, theoutput slices are passed by master control component 280 to displaycontrol component 284, which is configured to send control signals toLCD 5 to turn individual pixels of pixel array 256 on or off inaccordance with the pattern corresponding to an image slice transmittedby the display control component 284.

During a printing operation, the slices (image files) are transmitted bydisplay control component 284 (through the display adapter 214) to ascalar board 252 of the LCD 5. A scalar board is a standard and widelyused method of interfacing with displays. Typically, scalar boards areembedded as part of the electronics assembly inside commerciallyavailable LCD monitors or televisions. The scalar board 252 translatesan image or video file from digital signal (HDMI or DVI) or analoguesignal (VGA) into low voltage differential signals (LVDS) which areinterpretable by an internal control board 254 of the LCD 5. Internalcontrol board 254 switches pixels of the pixel array 256 on or off inaccordance with the input image received from the display controlcomponent 284.

During printing, the computer system 201 also interfaces, via a USB orserial interface (such as an RS-232 interface) with a microcontroller270 which is capable of driving all other actuators of the additivemanufacturing device. For example, the microcontroller 270 may drivestepper motors 21, the light source of radiation module 10 or 60, one ormore pumps (not shown) for pumping additional polymerizable medium 40 or51 into the vessel 1 or 50, linear or rotational motion actuators fordriving motion of vessel 50 and/or build platform 70 and/or radiationmodule 60, and so on. Microcontroller 270 may also read input fromvarious sensors, such as a level sensor for polymerizable material inthe vessel, a build platform height sensor, lateral sliding travelend-stop sensor(s) for vessel 50 and/or build platform 70 and/orradiation module 60, vertical end-stop sensors, temperature sensors, ahatch-closed sensor for support 22, and so on.

After each layer (slice image file) is sent from the display controlcomponent 284 to the scalar board 252 and thus projected on the display5 for the required curing time (which may be provided as one of thebuild parameters and/or determined according to the intensity andemission spectrum of the light source, and the nature of thepolymerizable medium) the master control component 280 may instruct,with appropriate timing and sequencing, mechanical actuation component286 and optical control component 288 to send signals to themicrocontroller 270 which can interpret them and drive the variousmotors, pumps and light source in the desired sequence.

An exemplary additive manufacturing method implementable using theadditive manufacturing device 500 of FIG. 5A to 5C or the additivemanufacturing device 550 of FIGS. 5D and 5E is depicted in FIG. 9. Atstep 810, mechanical actuation component 286 sends a signal tomicrocontroller 270 to move the build platform 70 to its startingposition. If necessary, at step 820 the radiation assembly 60 is movedto a starting position (again, via mechanical actuation component 286)such that a thin layer of polymerisable material is defined between thebuild surface of the build platform 70 and the radiation assembly 60.

At step 830, the radiation source of radiation assembly 60 is switchedon by optical component 288, and the pixel array 256 of LCD 5 iscontrolled in accordance with a desired pattern corresponding to a firstimage slice of the object to be built, by display control component 284as discussed above. In embodiments where the radiation assembly 60comprises an LED pixel array, then the radiation source need not beswitched on separately since the display control component 284 cansimply project the desired pattern directly from the LED pixels. As aresult of the patterned radiation, the thin layer of polymerisablematerial polymerizes in the regions which are exposed to radiation (step840).

Once the thin layer is cured in the desired manner, the pixel array 256and/or radiation source are switched off (step 850) by display controlcomponent 284 and/or optical component 288. Next, at step 860, theradiation assembly 60 and/or the vessel 50 may pivot relative to thebuild platform 70 (or vice versa) about hinge 53 in order to release thecured layer from a contact surface at the vessel 50 surface or theradiation assembly 60 surface.

To position the device 500 or 550 to polymerise the next layer of theobject, at step 870 the mechanical actuation component 286 sends acontrol signal to an actuator of build platform 70 or an actuator ofradiation assembly 60, via microcontroller 270, in order to move thebuild platform 70 vertically relative to the radiation assembly 60 by anamount equal to the desired layer thickness. This causes a new thinlayer of polymerisable material to fill a void left between thepreviously cured layer and the radiation assembly 60. Steps 820 to 880are repeated for each layer of the object to be built. Finally, at step890, mechanical actuation component 286 may send a signal to theactuator of build platform 70 in order to move the build platform 70 toa position where a user may easily remove the finished object from thebuild surface.

An alternative embodiment of an additive manufacturing method, forexample, implementable by the additive manufacturing device 600 of FIG.6A to 6C or the additive manufacturing device 650 of FIGS. 6D and 6E, isshown in FIG. 10.

The method 900 is in many respects similar to method 800. At step 910,mechanical actuation component 286 sends a signal to microcontroller 270to move the build platform 70 to its starting position. If necessary, atstep 920 the radiation assembly 60 is moved to a starting position(again, via mechanical actuation component 286) such that a thin layerof polymerisable material is defined between the build surface of thebuild platform 70 and the radiation assembly 60.

At step 930, the radiation source of radiation assembly 60 is switchedon by optical component 288, and the pixel array 256 of LCD 5 iscontrolled in accordance with a desired pattern corresponding to a firstimage slice of the object to be built, by display control component 284as discussed above. In embodiments where the radiation assembly 60comprises an LED pixel array, then the radiation source need not beswitched on separately since the display control component 284 cansimply project the desired pattern directly from the LED pixels. As aresult of the patterned radiation, the thin layer of polymerisablematerial polymerizes in the regions which are exposed to radiation (step940).

Once the thin layer is cured in the desired manner, the pixel array 256and/or radiation source are switched off (step 950) by display controlcomponent 284 and/or optical component 288.

Next, at step 960, mechanical actuation component 286 sends an actuationsignal to move the radiation assembly 60 and/or the vessel 50 laterallyrelative to the build platform 70 (or vice versa) in order to releasethe cured layer from a contact surface at the vessel 50 surface or theradiation assembly 60 surface by a shearing motion as previouslydescribed.

To position the device 500 or 550 to polymerise the next layer of theobject, at step 970 the mechanical actuation component 286 sends acontrol signal to an actuator of build platform 70 or an actuator ofradiation assembly 60, via microcontroller 270, in order to move thebuild platform 70 vertically relative to the radiation assembly 60 by anamount equal to the desired layer thickness. This causes a new thinlayer of polymerisable material to fill a void left between thepreviously cured layer and the radiation assembly 60. Steps 920 to 980are repeated for each layer of the object to be built. Finally, at step990, mechanical actuation component 286 may send a signal to theactuator of build platform 70 in order to move the build platform 70 toa position where a user may easily remove the finished object from thebuild surface.

Although particular embodiments have been described and illustrated, itwill be appreciated by those of ordinary skill in the art that variousmodifications and combinations of features of the above embodiments arepossible without departing from the scope of the invention as defined inthe appended claims.

1. An additive manufacturing device, comprising: a vessel for containinga material which is polymerisable on exposure to radiation; a buildplatform having a build surface, the build platform being mounted ormountable for movement relative to the vessel; and a programmableradiation module comprising an array of individually addressableradiation emitting or transmitting elements, the array beingconfigurable to produce radiation having a predetermined pattern byselective activation of elements of the array; wherein the programmableradiation module is positioned or positionable to irradiate uncuredmaterial adjacent the build surface, or adjacent a previously curedstructure on the build surface, with the predetermined pattern withoutmagnification.
 2. An additive manufacturing device according to claim 1,wherein the vessel has a transparent lower wall towards which the buildsurface faces, and wherein the radiation module is positioned toirradiate upwardly through the transparent lower wall.
 3. An additivemanufacturing device according to claim 1, wherein the radiation moduleis attached to or is integral with the vessel.
 4. An additivemanufacturing device according to claim 1, wherein the radiation modulecomprises a dynamic mask component containing the electronicallyaddressable array, and a radiation source for irradiating through thedynamic mask component.
 5. An additive manufacturing device according toclaim 4, wherein the dynamic mask component is attached to or isintegral with the vessel.
 6. An additive manufacturing device accordingto claim 4, wherein the dynamic mask component comprises a liquidcrystal display (LCD).
 7. An additive manufacturing device according toclaim 6, wherein the LCD is a monochrome LCD.
 8. An additivemanufacturing device according to claim 1, wherein the radiation modulecomprises an LED array or OLED array.
 9. An additive manufacturingdevice according to claim 1, wherein the vessel comprises a non-sticklayer or polymerization-inhibiting layer between the radiation moduleand the build platform.
 10. An additive manufacturing device accordingto claim 9, wherein the non-stick layer is formed from a silicone-basedmaterial.
 11. An additive manufacturing device according to claim 1,comprising a pivoting mechanism for allowing relative rotation betweenthe vessel and/or the radiation module on the one hand, and the buildplatform on the other hand.
 12. An additive manufacturing deviceaccording to claim 1, wherein the vessel comprises a curing regionadjacent to which the radiation module is positioned or positionable,and a separation region adjacent the curing region, the separationregion having a depth different to that of the curing region; andwherein the device comprises a linear translation mechanism for changingthe relative positions of the build platform and the radiation modulesuch that the build platform or the radiation module is moveable fromthe curing region to the separation region.
 13. An additivemanufacturing method, comprising: at least partially filling a vesselwith a material which is polymerisable on exposure to radiation;providing a programmable radiation module comprising an array ofindividually addressable radiation emitting or transmitting elements;providing a build platform having a build surface; positioning the buildplatform relative to the vessel such that an uncured layer ofpolymerisable material is defined between the build surface and theprogrammable radiation module; and irradiating the uncured layer ofpolymerisable material with radiation having a predetermined pattern,without magnification, by selectively activating elements of the arrayof the programmable radiation module in order to polymerise the uncuredlayer with the predetermined pattern.
 14. An additive manufacturingmethod according to claim 13, wherein the vessel has a transparent lowerwall towards which the build surface faces, and wherein the methodcomprises irradiating the uncured layer upwardly through the transparentlower wall.
 15. An additive manufacturing method according to claim 13,wherein the radiation module comprises a dynamic mask componentcontaining the electronically addressable array, and a radiation sourcefor irradiating through the dynamic mask component.
 16. An additivemanufacturing method according to claim 15, wherein the dynamic maskcomponent comprises a liquid crystal display (LCD).
 17. An additivemanufacturing method according to claim 16, wherein the LCD is amonochrome LCD.
 18. An additive manufacturing method according to claim13, wherein the vessel comprises a non-stick layer orpolymerization-inhibiting layer between the radiation module and thebuild platform.
 19. An additive manufacturing method according to claim13, comprising releasing the polymerized layer from a contact surface bypivoting the vessel and/or the radiation module relative to the buildplatform, or vice versa.
 20. An additive manufacturing method accordingto claim 13, comprising releasing the polymerized layer from a contactsurface by horizontally translating the vessel and/or the radiationmodule relative to the build platform, or vice versa.